The reliability and lifetime of machines using electronic components such as semiconductor devices can be increased by reducing the temperature variations imposed on the electronic components during operation. Therefore, electronic components often require a heat transfer device for cooling during normal operation. Heat exchangers have been used to transfer heat away from electronic components. A heat pipe, for example, thermally connects electronic components to the environmental ambient air with a low thermal resistance.
The elements of a heat pipe are a sealed container (pipe and end caps), a wick structure, and a small amount of working fluid which is in equilibrium with its own vapor. The length of the heat pipe is divided into three parts: evaporator section, adiabatic (transport) section, and condenser section. A heat pipe can have multiple heat sources or sinks with or without adiabatic sections depending on specific applications and design. Heat applied to the evaporator section by an external source is conducted through the pipe wall and wick structure where it vaporizes the working fluid. The resulting vapor pressure drives the vapor through the adiabatic section to the condenser, where the vapor condenses, releasing its latent heat of vaporization to the provided heat sink. Capillary pressure created by menisci in the wick pumps the condensed fluid back to the evaporator section.
During cold weather operation, such as at temperatures below zero degrees Celsius, a heat pipe can become nonfunctional when the working fluid freezes inside the condenser section of the heat pipe and causes an unacceptable rise in the thermal impedance of the heat pipe.